The present invention relates to variable valve actuating mechanisms.
Modern internal combustion engines may incorporate advanced throttle control systems, such as, for example, intake valve throttle control systems, to improve fuel economy and performance. Generally, intake valve throttle control systems control the flow of gas and air into and out of the engine cylinders by varying the timing and/or lift (i.e., the valve lift profile) of the cylinder valves in response to engine operating parameters, such as engine load, speed, and driver input. For example, the valve lift profile is varied from a relatively high-lift profile under high-load engine operating conditions to a reduced/lower low-lift profile under engine operating conditions of moderate and low loads.
Intake valve throttle control systems vary the valve lift profile through the use of variously-configured mechanical and/or electromechanical devices, collectively referred to hereinafter as variable valve actuation (VVA) mechanisms. Several examples of particular embodiments of VVA mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is hereby incorporated herein by reference.
Generally, a conventional VVA mechanism includes a rocker arm that is displaced in a generally radial direction by an input cam of a rotating input shaft, such as the engine camshaft. A pair of link arms transfers the displacement of the rocker arm to pivotal oscillation of a pair of output cams relative to the input shaft or camshaft. Each of the output cams is associated with a respective valve. The pivotal oscillation of the output cams is transferred to actuation of the valves by cam followers, such as, for example, direct acting cam followers or roller finger followers.
A desired valve lift profile is obtained by orienting the output cams in a starting or base angular orientation relative to the cam followers and/or the central axis of the input shaft. The starting or base angular orientation of the output cams determines the portion of the lift profile thereof that engages the cam followers as the output cams are pivotally oscillated, and thereby determines the valve lift profile. The starting or base angular orientation of the output cams is set via a control shaft that pivots a pair of frame members and, via the rocker arm and link arms, pivots the output cams to a base angular orientation that corresponds to the desired valve lift profile.
A conventional VVA mechanism is typically disposed between and actuates a pair of functionally corresponding valves, such as, for example, a pair of intake valves, of an engine cylinder. Thus, the rocker arm, link arms, output cams, and frame members of the VVA mechanism must all be accommodated within the space between the corresponding valves. However, cam support bearings are also conventionally disposed between the valves of each cylinder. Locating the cam support bearings between the valves places the bearings more proximate to deflection forces imposed upon the camshaft that result from valve actuation, and thereby provides the camshaft with additional stiffness. Further, locating the cam support bearings between the valves enables the cylinder head bolts to be located more conveniently.
In order to accommodate VVA mechanisms, however, engine cylinder heads must typically be redesigned to relocate the cam support bearings. More particularly, the cam support bearings are typically relocated from between the valves of each cylinder to a position between the cylinders in order to accommodate the VVA mechanisms in the spaces between the valves. Similarly, the cylinder head bolts must also be relocated. Relocating the cam bearings reduces camshaft stiffness and thereby potentially results in undesirable deflection of the camshaft. Relocating the cylinder head bolts may also be problematic in that a less effective coupling of the cylinder head to the engine may result.
Therefore, what is needed in the art is a VVA mechanism that is configured for being installed between adjacent engine cylinders.
Furthermore, what is needed in the art is a VVA mechanism that is installed within an engine without requiring relocation of the cam support bearings.
Moreover, what is needed in the art is a VVA mechanism that is installed within an engine without requiring relocation of the cylinder head bolts.
The present invention provides a variable valve actuation mechanism that is configured for being disposed between adjacent engine cylinders, and thus does not require relocation of the cam support bearings or the cylinder head bolts.
The invention comprises, in one form thereof, an output cam having a first output cam lobe and a second output cam lobe. A body portion adjoins and axially separates the first and second output cam lobes. The body portion includes an outer surface. A portion of the outer surface is configured for being pivotally engaged by a cam support bearing.
An advantage of the present invention is that it is operably disposed between adjacent engine cylinders and thus does not require the cam support bearings to be relocated.
A further advantage of the present invention is that it does not require relocation by of the cylinder head bolts.